Teachers have been stopped from using Zoom in Singapore following a series of "very serious incidents".
One incident reportedly saw hackers hijack the livestream of a geography lesson for teenage girls - forcing pictures of male genitalia to appear on their screens.
According to Straits Times, the attackers also made lewd remarks to the students, who were just 13 years old.
The security breaches came during the first week of a coronavirus lockdown in Singapore, which has seen many schools move to home-based learning.
Officials have warned they will file police reports if they track down the people who are responsible.
Zoom is a video conferencing app that has enjoyed an explosion in popularity as schools and offices close their doors, and families try to stay connected.
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But the company has been plagued with safety and privacy concerns, with frequent reports of "Zoom bombing": uninvited guests crashing meetings.
Germany and Taiwan have placed restrictions on the app's use - and one school in the US has stopped using Zoom altogether after a "naked adult male using racial slurs" intruded on a password-protected meeting.
Singapore says its suspension is a precautionary measure, and teachers will be able to carry on using Zoom if security issues are ironed out.
Zoom has embarked on a 90-day plan to tackle privacy and security issues - enlisting the help of a former Facebook security chief as it attempts to regain credibility.
The app was banned by the UK's Ministry of Defence last month, but high-level talks between the prime minister and his cabinet were held on the service days later.
"It is astounding that thousands of MoD staff have been banned from using Zoom only to find a sensitive government meeting like that of the prime minister's cabinet is being conducted over it," a source told Sky News at the time.